Certain thermoplastic polymer compositions include at least two phases: a continuous (matrix) phase and a discontinuous (dispersed) phase distributed within the matrix phase. A variety of such compositions have been proposed or prepared, including but not limited to thermoplastic olefin compositions (TPOs) and thermoplastic vulcanizates (TPV).
TPOs are typically blends that include polypropylene, modifier and optionally non-polymeric components such as fillers and other compounding ingredients. TPOs are multiphase polymer blends in which the polypropylene forms a continuous matrix phase and the modifier component, frequently derived from an ethylene-containing interpolymer, is the dispersed component. The polypropylene matrix provides tensile strength and chemical resistance to the TPO, while the ethylene polymer imparts flexibility and impact resistance. Usually, the dispersed phase of a TPO is not, or only modestly, cross-linked.
Thermoplastic vulcanizates (TPVs), regarded herein as a type of TPO, are also blends of polypropylene, modifier and optionally non-polymeric components such as fillers and other compounding ingredients.
Thermoplastic vulcanizates (TPVs) may be characterized by finely divided rubber particles dispersed within a plastic matrix. These rubber particles are crosslinked to promote elasticity. As such, TPVs exhibit the processing properties of the plastic and the elasticity of the rubber. A TPV differs from other TPOs primarily in that the dispersed modifier component is crosslinked, preferably “vulcanized,” to provide a rubber-like resilience to the composition. As a result of the increased coherence of the dispersed, crosslinked modifier, its share of the total composition is often increased to levels higher than for other TPOs. TPVs are conventionally produced by dynamic vulcanization. Dynamic vulcanization is a process whereby a rubber component is crosslinked or vulcanized within a blend of at least one non-vulcanizing polymer component while undergoing mixing or masticating at some elevated temperature. Preferably, the temperature of this curing step is greater than the melt temperature of the non-vulcanizing polymer component.
U.S. Pat. No. 6,245,856 describes a TPO comprising: a) 88 to 50 wt. % polypropylene, said polypropylene having a melt flow rate of 20 to 100 g/10 min, (ASTM D 1238, Condition L); b) at least 10 wt. % elastomer wherein said elastomer is selected from the group consisting of ethylene-C3 to C20 α-olefin elastomers and ethylene-C4 to C20 α-olefin-C4 to C20-diene elastomers; c) 2 to 15 wt. % of a compatibilizer having a number average molecular weight of 40,000 to 300,000 and comprising a ethylene-propylene copolymer having a propylene content of 80 to 92 wt. %. Component c) may be a propylene based elastomer and improves the performance of the composition. Such a TPO is a multiphase polymer blend in which the polypropylene a) forms a continuous matrix phase and the modifier component is the dispersed component. The polypropylene matrix tends to impart tensile strength and chemical resistance to the TPO, while the ethylene polymer tends to impart flexibility and impact resistance. In some cases the TPOs may have a dispersed phase which is not, or is only modestly, cross-linked. In other cases the impact modifying phase may be highly cross-linked permitting the use of higher amount of the elastomeric component and overall more rubbery characteristics. See U.S. Pat. No. 6,288,171. The dispersed modifier component is typically cross-linked or “vulcanized” to provide a rubber-like resilience to the composition, generally assisted by the presence of the diene in the impact modifying component. Neither of the aforementioned '856 or '171 patents disclose physically blending two polymer components one component being a reactor blend.
TPVs have been used to form composite structures for use in automotive, industrial, and consumer markets. Some of those uses require the adhesion of a TPV component to other materials to form a completed structure. Sufficient adhesion of which is difficult to obtain and difficult to maintain depending on the materials to be adhered, the adhering conditions, as well as the environment or conditions of use.
For example, WO 02/051634 discloses a two component composite structure where one of the polymer structures is made of EPDM blended with an effective amount of semicrystalline random adhesive copolymer, and the other polymer structure is made of a blend of dynamically vulcanized EPDM dispersed in a matrix of a thermoplastic polyolefin polymer. WO 02/051634 also discloses that the second polymer structure may be blended with the semicrystalline random adhesive copolymer. EP 0 601 790 discloses a two-layer sheet where each layer is made from an α-olefin copolymer rubber and a polyolefin resin. The first layer or “skin layer” is partially crosslinked, and the second layer or “back surface layer” is non-crosslinked. EP 0 601 790 discloses that the polyolefin resin is a homopolymer of ethylene or propylene, or copolymers of ethylene or propylene with small amounts of other polymeric monomers. Reactor blends comprising different polymeric species made either in a single polymerization zone using different catalysts or in separate polymerization zones, in which the species are mixed in solution before their separation from the polymerization diluent and formation of polymer pellet or bale have been described in U.S. Pat. Nos. 6,329,477; 6,319,998; 6,207,756; 6,545,088 and WO 03/040201.
None of those patents disclose physically blending the reactor blends with a polypropylene to form a new composition. Pellets formed from TPO or TPV compositions are often soft and tacky, and such properties are undesirable for storage and handling purposes. Also, there is an unfortunate tendency for the pellets to agglomerate, even when stored at ambient temperature. It would be desirable for pellets formed from a TPO or TPV composition to avoid such tackiness. It is among the objects of the invention to provide TPO and TPV composition which can be produced more economically and have an improved balance of properties.